Known shaking tables consist of sloped deck, or the upper bight of a moving belt, with or without superficial riffles and with means to vibrate the deck. The collective effect of deck motion, deck slope, deck surface, riffle configuration, rates of flow of material and wash medium, deck geometry and interaction of the material being treated with the wash medium, combine to achieve separation of the material into its components. The behaviour of such tables is in practice unpredictable owing to the inability to alter the variable parameters individually to meet the process conditions.
As a result, all shaking tables in current use that are known to the applicant are necessarily a compromise. Where deck motions imposed by linear vibration generate discontinuous shear forces, by the very nature of asymmetric or reciprocal motion, particle deceleration and remixing of the separated fractions occur. Where shaking is caused by rotation of an out-of-balance shaft, an unpredictable elliptical path is imposed on the particles traversing the deck and there is a control problem where the frequency of the oscillatory motion approaches the natural frequency of the table supports. In the latter case, the rate of shear is a function of at least three variables, viz rotational speed, amplitude and total shaken weight.
Adjustments to deck pitch are limited to either longitudinal or transverse slope, or both, but do not compensate for change with pitch of the approach angle of the stream of material to the riffles.
As far as the applicant is aware, no method has been used which yields an operation under continuous discharge with discrete control of any single variable which influences the separation and concentration of materials containing fractions within the range of densities.